Method of communicating in wireless network

ABSTRACT

A wireless network includes a current coordinator, at least one device which is currently associated with the wireless network, and a device selected as a new coordinator among the at least one device by the current coordinator. The current coordinator transmits a handover request message to the new coordinator; receives a handover response message in response to the handover request message from the new coordinator, the handover response message including a reason code field that is set to “success”; and broadcasts one or more beacons, each beacon including identification information which identifies the new coordinator and number information which indicates a number of remaining beacons that the current coordinator will broadcast before a handover occurs. The number information included in a last beacon among the one or more beacons is set to “0,” and the new coordinator broadcasts a beacon after receiving the last beacon from the current coordinator.

TECHNICAL FIELD

The present invention relates to wireless communication, and moreparticularly, to a method of performing communication for wirelessnetwork handover and implicit handover in wireless network.

BACKGROUND ART

Generally, various devices are peripherally used more often. So, thosedevices need to be used in a manner of interoperating with each other.Yet, it is inconvenient to connect a plurality of the devices togetherby wire. Since applications of the respective devices are not mutuallycompatible, it is substantially difficult to connect the devicestogether.

If communication is carried out by wireless technology, wires includingcable and the like between the devices can be removed. And, it is alsopossible to directly exchange data information in a manner that thedevices configure networks via wireless network between themselves.

Devices capable of performing communication on the network includecomputers, PDA, notebook computers, digital TV, camcorders, digitalcameras, printers, microphones, speakers, headsets, barcode readers,displays, mobile phones, and the like. And, all kinds of digital devicescan be used as the devices capable of performing communication on thenetwork.

In order to perform communication via the wireless network, a devicecapable of performing a control function of controlling and distributingresource allocation between devices configuring the network is needed.

If the device is unable to perform the control function as acoordinator, a process for enabling the control function to be performedby another device corresponding to one of the devices configuring thenetwork is needed.

Even if a new device having conditions better than those of a currentcoordinator in performing the control function is associated in thenetwork, a process for transferring the control function to the newdevice is needed as well.

Besides, when the process for transferring the control function is notperformed, it may happen that power supply to the coordinator issuddenly interrupted or that the coordinator moves away to deviate froma distance range for establishing the network.

However, under the above circumstances, if a device capable ofcontinuing the control function fails to exist, it is unable to make aresponse to resource allocation request from the devices in the courseof communication on the network. And, it is unable to perform a timingcontrol.

Accordingly, the devices performing the communication via the networkare unable to perform data transmissions and receptions. And, a problemof failing to maintain the network takes place.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the present invention is directed to a method ofcommunicating in wireless network that substantially obviates one ormore of the problems due to limitations and disadvantages of the relatedart.

An object of the present invention is to provide a method of maintaininga control function continuously, by which wireless communication can besmoothly carried out for the related art.

Another object of the present invention is to provide a method ofmaintaining a network coordinating function continuously, by whichwireless communication can be smoothly carried out for the related art.

Technical Solution

A device attempting to perform communication on a wireless networksearches channels on a band for performing communication and checks apresence or non-presence of a previously established network and thelike.

And, the device is associated in a previously established network andthen performs communication.

Moreover, the device can configure a new network by itself. Inconfiguring a new network, the device configures the new network in amanner of selecting a channel having a good channel environment based oninformation acquired from the above search and check processes and thenbroadcasting control information packets via the selected channel.

Even if a network including a control device is established, it mayhappen that the control device is unable to perform a control functiondue to user's necessity or environmental situations. If so, smoothcommunication of the network can be secured by a process fortransferring the control function to another device.

In case that a device more suitable to perform the control function thana current control device is associated in a network, it is preferablethat the control function is transferred to the newly associated devicefor smoother communication.

Thus, after a network has been established, a control device transfers acontrol function to another device. This is called a handover. Ahandover method according to one embodiment of the present invention isprovided. In particular, a method of deciding a device for making arequest for the handover according to a priority for a prescribedcontrol function is provided.

According to another embodiment of the present invention, in case that adevice for controlling communication resources of each device in awireless network system terminates its function without performing aprocess for handing over the control function, a method of continuingcommunication by recovering the control function is disclosed. In casethat the control function is suddenly terminated, the control functionin the network is maintained and recovered according to the presentembodiment. This can be named a recovery or an implicit handover.

Besides, a preliminary handover process can be executed prior toexecution of a handover or recovery operation. The preliminary handoverprocess means a process that a current coordinator transmits handoverrelevant information and/or coordinator relevant information to a deviceas a handover target and that the corresponding device stores thereceived handover relevant information and/or the received coordinatorrelevant information.

Advantageous Effects

According to one embodiment the present invention, communication can besmoothly carried out on a wireless network. In particular, communicationcan be seamlessly carried out without being considerably affected by asituation of a specific device.

And, a device capable of performing a coordinating function can beflexibly changed according to a situation instead of being specified toa specific device.

Moreover, a new coordinator is selected by considering a priority for acoordinating function to enable an optimal device to operate as the newcoordinator.

According to another embodiment the present invention, communication canbe smoothly carried out on a wireless network. In particular,communication can be seamlessly carried out without being considerablyaffected by a situation of a specific device.

And, a more suitable device can be selected in case of deciding asubstitute coordinator, whereby efficient communication is enabled.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a diagram of an example of WVAN including a plurality ofdevices;

FIG. 2 is a diagram for a hierarchical protocol structure implemented indevice of WVAN;

FIG. 3 is a flowchart of a process according to one preferred embodimentof the present invention;

FIG. 4 is a flowchart of a process according to another preferredembodiment of the present invention;

FIG. 5 is a flowchart of one example for a substitute coordinatordeciding method according to another preferred embodiment of the presentinvention; and

FIG. 6 is a flowchart of another example for a substitute coordinatordeciding method according to another preferred embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, An aspectof the present invention is in a coordinator in a wireless networkincluding the coordinator and at least one or more devices, a method ofperforming communication, comprising transmitting a handover requestmessage to a device having a highest priority for a coordinatingfunction among the at least one or more devices, transmittingcoordinator relevant information to the device, receiving a responsemessage including information indicating that the handover is acceptedin response to the handover request message and broadcasting a beaconincluding information indicating that the device becomes a newcoordinator.

In transmitting the handover request message to the device, if thedevice is newly associated in the network, the coordinator receivedinformation on the priority of the and the priority of the device ishigher than that of the coordinator; the handover request message may betransmitted to the device.

The coordinator relevant information may include at least one of currentrequests from the devices for CTBs, information about devices that arecurrently associated in the network including device capabilities,device IDs and power save statuses of the devices, and information onthe priority of each of the at least one or more devices.

The beacon may include at least one of information on the newcoordinator and information on a remaining time until the coordinatingfunction of the coordinator is terminated.

And the method may further comprise receiving a first beacon broadcastedby the device after a last beacons broadcasted by the coordinator.

And the method may further comprise rejecting a request messagetransmitted by another device associated in the network between a timingpoint at which the coordinator transmits a last beacon and anothertiming point at which the device transmits a first beacon.

Another aspect of the present invention is method of performingcommunication in a wireless network, which includes a coordinator, themethod comprising receiving information on a priority of a deviceassociated in the network, transmitting a handover request messageincluding coordinator relevant information to the device if the priorityof the device is higher than that of the coordinator, receiving aresponse message including information indicating that the handover isaccepted in response to the handover request message and broadcasting abeacon including information indicating that the device becomes a newcoordinator.

The priority may be decided according to a prescribed evaluationreference that includes a device feature of the device and a networksituation by at least one of the device and the coordinator.

The coordinator relevant information may include at least one of currentrequests from the devices for CTBs, information about devices that arecurrently associated in the network including device capabilities,device IDs and power save statuses of the devices, and information onthe priority of each of the at least one or more devices.

The method may further comprise receiving a first beacon broadcasted bythe device after a last beacon broadcasted by the coordinator.

Another aspect of the present invention is in a coordinator in awireless network including the coordinator and at least one or moredevices, a method of performing communication, comprising transmitting afirst handover request message including coordinator relevantinformation to a first device having a highest priority among the atleast one or more devices, receiving a response message includinginformation indicating a handover rejection in response to the firsthandover request message and transmitting a second handover requestmessage to a second device having a second highest priority among the atleast one or more devices.

Another aspect of the present invention is in a coordinator in awireless network including the coordinator and at least one or moredevices, a method of performing communication, comprising transmitting afirst handover request message including coordinator relevantinformation to a first device having a highest priority among the atleast one or more devices and if a response message in response to thefirst handover request message is not received for a predetermined time,transmitting a second handover request message to a second device havinga second highest priority among the at least one or more devices.

Another aspect of the present invention is in a coordinator in awireless network including the coordinator and at least one or moredevices, a method of performing communication, comprising selecting adevice having a highest priority as a secondary coordinator among the atleast one or more devices associated in the wireless network,transmitting a message announcing that the device having the highestpriority is specified as the secondary coordinator and transmittingcoordinator relevant information to the secondary coordinator, whereinthe device selected as the secondary coordinator operates as a newcoordinator in the wireless network in case of failing to receive abeacon from the coordinator at a beacon reception estimated timingpoint.

A device feature for deciding the priority may include at least one of anumber of other devices accessible by the device, a time for maintaininga power of the device, and a transmission power of the device.

Another aspect of the present invention is in specific device of awireless network including a coordinator and at least one or moredevices, a method of performing communication, comprising receiving abackup message instructing to be selected as a secondary coordinatorfrom the coordinator and in case of failing to receive a beacon from thecoordinator at a beacon reception estimated timing point, transmitting abeacon to the wireless network.

After receiving the backup message, the method may further comprisereceiving a beacon including coordinator relevant information from thecoordinator and storing the coordinator relevant information.

The specific device may be decided through a priority for a coordinatingfunction.

A device feature for deciding the priority may include at least one of anumber of other devices accessible by the device, a time for maintaininga power of the device, and a transmission power of the device.

A beacon broadcasted by the specific device may include information on anew coordinator.

Another aspect of the present invention is in specific device of awireless network including a coordinator and at least one or moredevices, a method of performing communication, comprising receiving abackup message instructing to be selected as a secondary coordinatorfrom the coordinator, in case of failing to receive a beacon from thecoordinator at a beacon reception estimated timing point, transmitting aconfirm message for confirming whether the coordinator can maintain acoordinating function to the coordinator and in case of failing toreceive a message in response to the confirm message for a prescribedtime, broadcasting a beacon to the wireless network.

The prescribed time may be a random access time block (RATB).

Another aspect of the present invention is in a wireless networkincluding a coordinator and at least one or more devices, a method ofperforming communication, comprising receiving a priority list for acoordinating function from the coordinator and broadcasting a beacon tothe network at a next beacon transmission timing by a device having ahighest priority on the priority list if the device is not received abeacon from the coordinator within a prescribed time.

The broadcasted beacon may include information indicating the device isa new coordinator.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

MODE FOR THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

Embodiments in the following description relate to examples that thetechnical features of the present invention are applied to WVAN(wireless video area network) as a sort of wireless network. The WVAN isa wireless network capable of providing throughput over 4.5 Gbps totransport 1080p A/V stream within a short range of 10 meters withoutcompression using a frequency band of 60 GHz.

FIG. 1 shows an example of WVAN including a plurality of devices.

The WVAN is a network configured for data exchange between deviceslocated in a predetermined space. The WVAN includes at least two or moredevices 10 to 14. And, one of the devices operates as a coordinator 10.In configuring a wireless network between the devices, a plurality ofthe devices should share radio resources with each other. To enable thedevices to share the radio resources without collision, the coordinator10 performs allocating and scheduling the radio resources.

The coordinator is provided with a function of allocating resources toenable the devices configuring the network to perform communication. Thecoordinator is also a normal device capable of transmitting andreceiving data via at least one channel. Moreover, the coordinator isable to perform such a function as clock synchronization, networkassociation, maintaining bandwidth resource, and the like as well.

The WVAN supports two kinds of physical layers (PHY). In particular, theWVAN supports HRP (high-rate physical layer) and LRP (low-rate physicallayer). The HRP is the physical layer capable of supporting a data rateover 1 Gb/s, and the LRP is the physical layer capable of supporting adata rate of several Mb/s. The HRP is highly directional and is used fortransmissions of isochronous data stream, asynchronous data, MAC commandand A/V data via unicast connection. And, the LRP supports directivityor an omni-directional mode and is used for transmissions of beacon,asynchronous data, MAC command including beacon, and the like viaunicast or broadcast. HRP channel and LRP channel share frequency bandwith each other and are discriminated in use from each other by TDM.

An example of a super frame structure used for the above-explained WVANis explained as follows.

First of all, each super frame includes an area for transmitting beacon,a reserved channel time block, and an unreserved channel time block. Thebeacon is periodically transmitted to identify an introduction part ofeach super frame. The beacon packet includes scheduled timinginformation and management and control information on the WVAN. Thedevice is capable of data exchange on the network through the timinginformation, the management/control information and the like included inthe beacon. And, contention-based control period (CBCP) located next tothe beacon is included to transmit an urgent control/management message.The contention-based control period can be named random access timeblock (RATB). A period length of the RATB is set to a predeterminedthreshold (mMAXCBCPLen) not to exceed.

FIG. 2 is a diagram for a hierarchical protocol structure implemented indevice of WVAN.

Referring to FIG. 2, each device included in WVAN can be divided into atleast two layers according to its function and generally includes a PHYlayer 21 and a MAC layer 20.

The device includes entities managing the layers, respectively. Theentity managing the MAC layer is called MLME (MAC layer managemententity) 200. And, the entity managing the PHY layer is called PLME (PHYlayer management entity) 210.

And, the device includes a device management entity (DME) 220 thatcollects status information on each device and plays a role as a controlpath (interface) between a host and a wireless device. A messageexchanged between layers different from each other is called aprimitive.

The WVAN is initiated when a coordinator broadcasts a beacon. The devicecan perform communication in a manner that a channel time block for dataexchange is allocated through an association procedure with thecoordinator.

A method of performing communication for handover according to oneembodiment of the present invention is explained as follows.

FIG. 3 is a flowchart of a process according to one preferred embodimentof the present invention.

As a random device broadcasts a beacon, a network is established. And,the random device becomes a coordinator in the network.

If the coordinator moves away from the network or a power is cut off,the coordinator is unable to perform a coordinating function any more.If so, handover is executed. The coordinator selects another device thatconfigures the network. In this case, the selected device should be ableto perform a coordinating function at least.

In selecting one from devices configuring the network to make a handoverrequest thereto, a priority is given to each of the devices to select adevice in a better environment. In particular, the coordinator receivesinformation on priorities for coordinating functions of the devicesincluded in the network and then selects a device in an optimalcondition to play a role as a new coordinator in performing handoverusing the priority information for the coordinating functions. Thepriority on the coordinating function is decided in a manner ofdetermining evaluation references for time, place and the like and thenconsidering device characteristics for the evaluation references.

In particular, each of the devices is able to decide a priority numberfor its coordinating function by considering such a fact as a long-lifetime feature, a power remaining quantity, a battery or an AC power, anetwork-coverage feature (which indicates how many devices capable oftransmitting control messages and the like), and the like.

The coordinator receives the priority information (number) on thecoordinating function of each of the devices and then configures andstores a list. In this case, the list configured through the priorityinformation on the coordinating function can be called CCD (coordinatorcapable device) list.

Preferably, in transmitting a handover request message, the coordinatortransmits a request message to the aforesaid device having the highestpriority rather than transmits a request message to a random device. Inparticular, if the handover request message is preferentiallytransmitted to the device having the highest priority in accordance withthe priority for the coordinating function, an optimal device canperform the coordinating function within an available range.

The DME of the coordinator transmits a MLME-CO-ORDINATOR-HANDOVER.reqprimitive to the MLME to make a request for handover to the selecteddevice (S300). The MLME of the coordinator transmits a handover requestmessage (Coordinator-Handover request) to MLME of the selected device(S310).

Having transmitted the handover request message, the coordinator is ableto transmit handover relevant information (information required forhandover) and/or coordinator relevant information (information requiredfor coordinating function execution).

For instance, information on a channel time currently reserved on anetwork, current requests from devices for CTBs, information on aremaining time until a current coordinator hands over a coordinatingfunction (e.g., a count of remaining beacons, a count of beaconintervals, etc.), information on options (features) of devicesconfiguring a current network (information about devices that arecurrently associated in the WVAN, e.g., capabilities, device ID, powersave statuses of devices, etc.), information on a coordinating functionpriority of each device, and the like may be transmitted to the selecteddevice together with the handover request message to be used for thedevice to decide whether to perform the handover. Besides, anyinformation necessary for the handover can be transmitted together withthe message for requesting the handover as well as the above-explainedinformation.

In case that no request is made by a device, if information needed toexecute handover is transmitted together with the handover requestmessage, a size of packets (data) to transported can be reduced. And, acorresponding procedure can be simplified as well. An example of MACcommand format included in the handover request message is proposed byTable 1.

TABLE 1 Octets: 1 1 1 1 variable Variable Variable command length Break-Time- IE (Re- IE IE ID (ex. ing-in out served (Device (CCD 0x0E) periodsched- list) list) ule)

Through the Breaking-in period field shown in Table 1, it is able toknow information on a time remaining until the device having receivedthe handover request message initiates an operation by working as a newcoordinator.

Through the timeout field, it is able to know information on a scheduletime at which the device having received the handover request messageshould transmit a handover response message in response to the handoverrequest message.

Through the reeserved schedule filed shown in Table 1, it is able toknow information on the reserved channel time.

Through the device list field, it is able to know information on devicesconfiguring the network.

Through the CCD list field, it is able to know priority information on acoordinating function.

Meanwhile, MLME of the device having received the handover requestmessage transmits a MLME-COORDINATOR-HANDOVER.ind primitive to DME toacknowledge that the request message has been received (S320).

The selected device decides whether to perform the coordinating functionand then transmits a handover response message in response to thehandover request message. In particular, the DME of the selected devicetransmits a MIME-CO-ORDINATOR-HANDOVER.rsp primitive to the MLME (S330).

The MLME of the selected device transmits the handover response message(Coordinator-Handover response) to the MLME of the coordinator (S340).An example of format of MAC command included in the handover responsemessage is proposed by Table 2.

TABLE 2 Octets: 1 1 command ID (ex. 0X0E) Reason code (ex. 0x00:success, 0x01-0xFE: failure)

The command format for the handover response message shown in Table 2includes the reason code field. In this case, the reason code representsinformation that indicates acceptance or rejection to become a newcoordinator. And, the coordinator is able to know success or failure ofthe handover request message using the reason code.

After the handover request message has been transmitted, it ispreferable that the handover response message corresponding to thehandover request message is received within a predetermined time. So,after the handover request message has been transmitted, the coordinatoractivates a timer set to the predetermined time. If a response messageis received before completion of the timer, the coordinator deactivatesthe timer (S350).

The coordinator transmits a handover request message includinginformation on the predetermined time to enable a device having receivedthe handover request message to transmit a handover response messagewithin the predetermined time (cf. Table 1). Yet, if the responsemessage is not received until the timer is completed, the handoverrequest fails. And, the handover request message will be transmitted toanother device configuring the network.

The MLME of the coordinator sends a MLME-CO-ORDINATOR-HANDOVER.cfmprimitive to the DME to indicate that the handover response message hasbeen received (S360).

The DME of the coordinator sends a MLME-BEACON.req primitive for beacontransmission to the MLME (S370).

The MLME of the coordinator broadcasts a beacon to the network (S380).If the handover request is successful, the coordinator transmitsinformation on a new coordinator, a CCD list, performance of devicesconfiguring a current network and the like in case of transmitting anext beacon.

An example of information element (IE) format for the informationtransmitted by being included in the beacon is explained as follows.Information indicating which IE will be used in accordance with aconfiguration of the MAC command or beacon can be included andtransmitted. And, a message is transmitted by the defined IE format.Examples of IE format indicating the information on the priority number(CCD list), IE format indicating information on capability of deviceconfiguring a current network (device capability list), and IE formatindicating information for a device decided as a new coordinator (newcoordinator information) are explained with reference to the followingtable.

Table 3 shows an example of IE format indicating information on prioritynumber (prioritized CCD list).

TABLE 3 Octets: 1 1 2 2 IE index IE length = n * 2 CCD list block CCDlist block

The IE format indicating the prioritized CCD list includes information(IE length) on a length of the IE format. If the count of devices(coordinator capable device: CCD) capable of performing the coordinatingfunction is n, the length can become n*2 octets.

An exemplary configuration of the CCD list block field is shown indetail in Table 4.

TABLE 4 1 1 CCD ID Priority Val

Referring to Table 4, the CCD list block field includes identificationinformation of each CCD (CCD ID) and a CCD list block includinginformation on a priority number.

Table 5 shows an example of the IE format indicating information oncapability of device configuring a current network (Device Capabilitylist).

TABLE 5 Octets: 1 1 3 3 IE index IE length = n * 3 MAC capability MACcapability Block 1 Block 1

In the IE format shown in Table 5, information indicating a length ofthe IE format (IE length) is included as well. If the count of devices(coordinator capable device: CCD) capable of performing the coordinatingfunction is n, the length can become n*3 octets.

An exemplary configuration of the MAC Capability Block field is shown indetail in Table 6.

TABLE 6 Octets: 1 2 Device ID MAC Capability Bitmap

Referring to Table 6, the MAC Capability Block field includes deviceidentification information (device ID) for each device configuring anetwork and MAC Capability Bitmap including information on devicecapability.

An exemplary configuration of the MAC Capability Bitmap is explained indetail with reference to Table 7 as follows.

TABLE 7 Bits: 1 1 1 1 12 Reserved Fast Link HRP TX HRP RX ReservedRecommendation

Referring to Table 7, the MAC Capability Bitmap allocates 1 bit to eachof information on a channel time reservation and information for fastlink (Fast Link Recommendation). And, 1 bit is allocated to indicate atransmitting/receiving side of HRP (high rate PHY) channelcommunication.

Table 8 shows an example of IE format indicating information on a devicedecided as a new coordinator (New Coordinator Information).

TABLE 8 Octets: 1 1 1 1 IE index IE length = 2 New coordinator IDRemaining breaking-in period

The IE format can include information indicating a length of the IEformat (IE length), identification information on a device decided as anew coordinator (New coordinator ID), and information on a remainingtime until a current coordinator transmits a last beacon (e.g.,remaining breaking-in period).

In order to announce when the device decided as the new coordinator canperform the coordinating function, the beacon can be transmitted in amanner of including information on a remaining time until a currentcoordinator transmits a last beacon. In this case, the remainingbreaking-in period field can be used.

If the breaking-in period, which remains until the coordinatorterminates the coordinating function after receiving the handoverresponse message, is n, a beacon including information of breaking-inperiod=n is transmitted. A next beacon including information ofbreaking-in period=n−1 is then transmitted. A last beacon includesinformation of breaking-in period=0. The new coordinator having receivedthe information transmits a first beacon from a next beacon transmissiontiming.

The informations are included in the beacon to be transmitted by thecurrent coordinator using the above-explained IE format. The beacon isthen transmitted. An example of a beacon message format including theinformations is proposed by Table 9.

TABLE 9 1 1 variable variable variable 4 Beacon CBCP end IE l IE m IE nCRC Control time

Referring to Table 9, the beacon message includes beacon controlinformation and information on a CBCP end timing point and also includesIE format information for the information necessary for the rest of thefields. So, the beacon message is able to transmit the necessaryinformations.

For instance, IE proposed by Table 8 is inserted in the IE 1 field totransmit information on a device decided as a new coordinator (NewCoordinator Information). The IE proposed by Table 3 is inserted in theIE m field to transmit information indicating a priority number(Prioritized CCD list). And, the IE proposed by Table 5 is inserted inthe IE n field to transmit information on capability of deviceconfiguring a current network (Device Capability list).

To inform that the beacon has been received, the MLME of the devicehaving received the beacon sends a MLME-BEACON.ind primitive to the DME(S390, S395).

Having received the last beacon transmitted by the current coordinator,the DME of the new coordinator sends a MLME-BEACON.req primitive to theMLME to transmit a beacon for a next beacon transmitting interval(S396).

The MLME of the new coordinator broadcasts a beacon to the network(S397).

The current coordinator having received the beacon sends aMLME-BEACON.ind primitive to the DME to inform that the beacon has beenreceived (S398).

For stable handover, the current coordinator transmits the last beaconand then remains on the network for a predetermined time to checkwhether a beacon transmitted by a new coordinator is received.Preferably, the beacon transmitted by the new coordinator is receivedwithin a predetermined time after the last beacon has been transmitted.

So, after a timer set to a predetermined time is activated aftercompletion of the last beacon, if a beacon message is received beforecompletion of the timer, the coordinator deactivated the time and thenterminates a coordinator role (S399). Yet, if the beacon message is notreceived until the timer is completed, the handover process fails. So, ahandover request message is transmitted to another device configuringthe network to re-execute the handover process.

Even if the handover request or the handover process fails, it ispreferable that another device is selected using the information on thepriority. More preferably, a handover request message is transmitted toa device having a priority higher than the former priority.

Preferably, for a time from a timing point of receiving a handoverapprove response message to a timing point of transmitting a lastbeacon, the current coordinator rejects request messages (e.g., channeltime assign request message, association request message, etc.)transmitted by other devices.

A recovery or implicit handover method, which maintains and recovers acontrol function in a network if the control function is suddenlyterminated, according to another embodiment of the present invention isexplained as follows.

For example of the recovery method, there is a method including thesteps of deciding a new control device before execution of a recoveryprocess and then enabling the new control device to perform recovery. Inthe following description, a device decided as the new control device isnamed a secondary controller or a secondary coordinator (SCD).

In case that the secondary coordinator recognizes that a controlfunction is abnormal, it transmits a request message to confirm whetheran old control device keeps operating or a function of the old controldevice is terminated. If a response message is not received from the oldcontrol device after completion of prescribed duration, the secondarycoordinator plays a role as a new control device in a network inperforming a control function.

FIG. 4 is a flowchart of a process according to another preferredembodiment of the present invention. WVAN, as shown in FIG. 1, includesa plurality of devices 10 to 14. And, one of a plurality of the devicesoperates as a coordinator 10. For clarity of explanation, FIG. 4 showsdevices in part.

Referring to FIG. 4, a DME of the coordinator sends a MLME-BEACON.reqprimitive for requesting a beacon transmission to an MLME (S400).

The MLME of the coordinator transmits a beacon to MLME of devicesconfiguring EVAN (S401).

An MLME of each of the devices having received the beacon sends aMLME-BEACON.ind primitive announcing that the beacon has been receivedto a DME of each of the devices (S402, S403).

The devices configuring the WVAN are able to perform data exchanges witheach other via scheduling information of the beacon.

If a power of the coordinator is cut off (S404) or if the coordinatormoves away from an area of the WVAN, it is impossible to perform abeacon broadcast any more. If so, the devices within the WVAN are unableto receive the beacon at a scheduled timing (S405, S406). Thus, the casethat a scheduled beacon is not received is named a case that a beacon ismissed.

To prepare for a case that the coordinator is unable to perform acoordinating function suddenly in WVAN communication, a secondarycoordinator (SCD) is decided in advance.

If a device decided as the secondary coordinator (hereinafter calledsecondary coordinator) is unable to receive the beacon (S406), a DME ofthe secondary coordinator sends a CTB-TIME-IE.req primitive, whichrequests to transmit a confirmation request message to a currentcoordinator, to a MLME (S407).

The MLME of the secondary coordinator transmits the confirmation requestmessage (CTB-TIME-IE req) to the MLME of the current coordinatoraccording to the primitive (S408).

Namely, if the beacon is not received from the current coordinator, thesecondary coordinator transmits the confirmation request message. If aresponse message in response to the request message is not received, thesecondary coordinator can decide that the corresponding coordinatingfunction is not executed.

It takes a prescribed time until it is decided whether a response to theconfirmation request message is received (S409). If the response messageis not transmitted from the current coordinator for the prescribed time,the secondary coordinator starts to operate as a new coordinator of theWVAN.

The DME of the secondary coordinator operating as a new coordinatorsends a MLME-BEACON.req primitive for a transmission of a beacon at anext beacon transmission timing (S410).

The MLME of the secondary coordinator broadcasts a beacon on a network(S411). In this case, a first transmitted beacon is configured toinclude information on a new coordinator and then transmitted (S411).

Each MLME of the devices receives the broadcasted beacon and then sendsa MLME-BEACON.ind primitive, which announces the beacon is received, tothe corresponding DME of each of the devices (S412).

One embodiment of a time reference for transmitting the confirmationrequest message and awaiting the response message is explained in detailas follows. A prescribed timer function is available. In particular, awaiting time is set, the timer is activated before or after transmissionof the confirmation request message, the timer is then terminated afterelapse of the time.

Preferably, the coordinator is able to use the structure of the superframe for timing control information on the channel time resource. Ifthe secondary coordinator fails to receive the beacon for a timing thatthe beacon should be transmitted, a timing information request messageis transmitted to the coordinator for RATB to make a request for timinginformation that could be provided by the beacon that is not received.In the recovery process, the confirmation request message (CM-TIME-IEreq) is transmitted using the RATB. If the secondary coordinator failsto receive the beacon at the timing of transmitting the beacon, theconfirmation request message (CTB-TIME-IE req) is transmitted for theRATB (S408).

FIG. 5 is a flowchart of one example for a substitute coordinatordeciding method according to another preferred embodiment of the presentinvention.

An example that a current coordinator decides a secondary coordinatorprior to a recovery process is explained with reference to FIG. 5. Thesecondary coordinator deciding step prior to the recovery process can bean example of a pre-handover process.

First of all, a coordinator selects a random device from a plurality ofdevices configuring WVAN. In this case, the selected device should beable to perform a coordinating function at least. A DME of thecoordinator sends a MLME-BACKUP.req primitive to a MLME to make a backuprequest (S500).

The MLME of the coordinator transmits a backup request message to a MLMEof the selected device (S502). The backup request message is a messagethat makes a request for the coordinator to select a random device as asecondary coordinator for performing a recovery in the future. A formatof MAC command usable in transmitting the backup request message isproposed by Table 10.

TABLE 10 Octets: 1 1 variable Command ID (ex. 0x10) length IE (devicelist)

A command format for a backup request message shown in Table 10 includesa filed for a device list. In this case, the device list is aninformation list about devices configuring a current network. Byincluding the device list in the backup request message and thentransmitting the message, it is able to use the included device list indeciding whether the selected device is going to become a secondarycoordinator.

Since a response message in response to the backup request message ispreferably received within a predetermined time, it is able to an elapseof the predetermined time via a timer. In particular, a timer set to thepredetermined time is activated before the backup request message istransmitted (S501). And, it is also able to activate the timer when therequest message is transmitted or after the request message has beentransmitted.

The activated timer completes its operation if the set time is up. So,it is able to know whether the predetermined time goes by.Alternatively, the coordinator transmits a backup request messageincluding information on the predetermined time. So, the coordinatorenables a device having received the backup request message to transmita backup response message within the predetermined time.

Before the timer expires, i.e., before the predetermined time goes by, aDME of the device having received the backup request message sends aMLME-BACKUP.rsp primitive for a backup message transmission to a MLME(S504).

The MLME of the device transmits a backup response message to the MLMEof the coordinator (S505). A format of MAC command usable intransmitting the backup response message is proposed by Table 11.

TABLE 11 Octets: 1 1 Command ID Reason code (ex. 0x00: success, 0x01 to0xEF: failure) (ex. 0x11)

A command format for a backup response message shown in Table 11includes a filed for a reason code. The reason code indicates a resultfor whether to accept to become a secondary coordinator for the backuprequest message. The coordinator is able to know success/failure of thebackup request message using the reason code.

If the backup response message is received, the timer stops operatingbefore its expiration (S511).

The MLME of the coordinator sends a MLME-BACKUP.cfm primitive to the DMEto announce that the backup response message has been received (S506).

If the backup response message of success is transmitted, the device isdecided as a secondary coordinator. The MLME of the coordinatortransmits a beacon to a MLME of the device decided as the secondarycoordinator (S508).

The device decided as the secondary coordinator stores informationincluded in the transmitted beacon to perform a coordinating function asa new coordinator after completion of a recovery process (S510).

According to another embodiment, it will be more preferable to make aselection by deciding a priority for a coordinating function of deviceand considering the priority rather than by selecting a random devicefrom a plurality of devices and then transmitting a backup requestmessage. Each of the devices differs in a suitable degree as acoordinator in accordance with device characteristics and features.

So, a priority for a coordinating function can be set up throughinformation for each device feature from the devices configuring thenetwork. By enabling the coordinator to know the setup priorityinformation or enabling the setup priority information to be shared bythe devices configuring the network, it is able to more properly decidewhich one of the devices is more suitable for a coordinator.

According to a further embodiment, a coordinator receives priorityinformation on the coordinating function from the devices and thenconfigures a priority list for the coordinating function. The configuredpriority list for the coordinating function is transmitted to eachdevice via an announcement message. Alternatively, the coordinatorreceives a message from requesting a list from each device and thentransmits the priority list for the coordinating function via a responsemessage in response to the message for requesting the list.

Each of the devices knowing the transmitted priority list for thecoordinating function becomes a secondary coordinator by itself and thenstores information necessary to perform the coordinating function, toprepare for an occurrence of a beacon miss. The device having become thesecondary coordinator can inform the coordinator that its is decided asthe secondary coordinator via an announcement message. If the secondarycoordinator fails to receive a beacon from the coordinator, it operatesas a new coordinator by transmitting a beacon by itself.

In deciding the priority, considerable features include a number ofother accessible devices according to locations of the respectivedevices, a time for continuing a power, an outputted power, and thelike.

FIG. 6 is a flowchart of another example for a substitute coordinatordeciding method according to another preferred embodiment of the presentinvention.

A selecting method proposed by FIG. 6 relates to a case that a backupresponse message of success is not transmitted in response to a backuprequest message transmitted by a coordinator. For clarity ofexplanation, FIG. 6 shows a MLME transmission message of device onlywithout representing a layer structure of each device. Yet, it isapparent that a signal exchange between layer structures should exist.

Referring to FIG. 6, the coordinator transmits a backup request message(Back-up Request) to a random first device (S601).

A method of checking whether a backup response message is transmitted bythe first device for a predetermined time is executed by the same methodproposed by FIG. 4. In particular, a timer is activated before thebackup request message is transmitted. After the predetermined time goesby, the timer expires (S600, S602).

The coordinator transmits a backup request message including informationon the predetermined time and then enables a device having received thebackup request message to transmit a backup response message within thepredetermined time. If a backup response message is not received fromthe first device or if a backup response message of failure is received,a secondary coordinator deciding process for the first device fails.

The coordinator transmits a backup request message (Backup Request) to asecond device again (S604). A deciding method for the second device canbe carried out by the same method proposed by FIG. 4 (S603 to S608).

In this case, the above-explained priority information on thecoordinating function between the devices is usable as well. Inparticular, after a backup request message has been preferentiallytransmitted to a device having a highest priority, if a backup responsemessage is not transmitted or a backup response message of failure istransmitted, a backup request message (Backup request) is transmitted toanother device having a second highest priority again. Thus, thesecondary coordinator is selected by considering the priority for thecoordinating function, whereby internetwork communication can be moreefficiently carried out.

According to one embodiment of the present invention, communication canbe smoothly carried out in a wireless network. Specifically,communication can be seamlessly carried out without being considerablyaffected by a situation of a specific device. A device performing acoordinating function is not limited to a specific device but can beflexibly changed according to a situation. Moreover, a new coordinatoris selected by considering a priority for a coordinating function,whereby an optimal device can operate as a new coordinator.

According to another embodiment of the present invention, communicationcan be smoothly carried out in a wireless network. Specifically,communication can be seamlessly carried out without being considerablyaffected by a situation of a specific device. Moreover, it is able toselect a more suitable device in deciding a secondary coordinator,whereby efficient communication is enabled.

Besides, the terminologies used in the above disclosure can be replacedby other terminologies. For instance, a device can be replaced by one ofa user device (or apparatus), a station and the like. A coordinator canbe replaced by one of a coordinating or control device, a coordinatingor control device, a coordinating or control station, a coordinator, aPNC (pico net coordinator) and the like.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

Accordingly, the present invention is applicable to wirelesscommunication. In particular, the present invention is applicable to ahandover in a wireless network or communication execution for animplicit handover.

1. A wireless network comprising: a current coordinator and at least onedevice which is currently associated with the wireless network; and adevice selected as a new coordinator among the at least one device bythe current coordinator, wherein the current coordinator is configuredto: transmit a handover request message to the new coordinator; receivea handover response message in response to the handover request messagefrom the new coordinator, the handover response message comprising areason code field that is set to “success”; and broadcast one or morebeacons, each of the one or more beacons comprising identificationinformation which identifies the new coordinator and number informationwhich indicates a number of remaining beacons that the currentcoordinator will broadcast before a handover occurs, wherein the numberinformation included in a last beacon among the one or more beacons isset to “0,” and wherein the new coordinator is configured to broadcast abeacon after receiving the last beacon from the current coordinator. 2.The wireless network of claim 1, wherein the current coordinator isfurther configured to transmit coordinator relevant information to thenew coordinator.
 3. The wireless network of claim 2, wherein thecoordinator relevant information comprises information about the atleast one device.
 4. The wireless network of claim 3, wherein thecoordinator relevant information further comprises informationassociated with current requests from the at least one device forchannel time blocks (CTBs).
 5. The wireless network of claim 3, whereinthe information about the at least one device comprises capabilities andan identifier of each of the at least one device.
 6. The wirelessnetwork of claim 1, wherein the current coordinator is furtherconfigured to receive the beacon broadcast by the new coordinator.
 7. Awireless network comprising: a coordinator; and at least one devicewhich is currently associated with the wireless network, wherein thecoordinator is configured to: receive, from a new device, informationassociated with a priority of the new device when the new device joinsthe wireless network; transmit a handover request message to the newdevice if the priority of the new device is higher than a priority ofthe coordinator based on the information received from the new device;receive a handover response message in response to the handover requestmessage from the new device; and broadcast one or more beacons, each ofthe one or more beacons comprising identification information whichidentifies the new device and number information which indicates anumber of remaining beacons that the coordinator will broadcast before ahandover occurs, wherein the number information included in a lastbeacon among the one or more beacons is set to “0,” and wherein the newdevice is configured to broadcast a beacon as a new coordinator afterreceiving the last beacon from the coordinator.
 8. The wireless networkof claim 7, wherein the coordinator is further configured to transmitcoordinator relevant information to the new device.
 9. The wirelessnetwork of claim 8, wherein the coordinator relevant informationcomprises information about the at least one device.
 10. The wirelessnetwork of claim 9, wherein the coordinator relevant information furthercomprises information associated with current requests from the at leastone device for channel time blocks (CTBs).
 11. The wireless network ofclaim 9, wherein the information about the at least one device comprisescapabilities and an identifier of each of the at least one device. 12.The wireless network of claim 7, wherein the handover response messagecomprises information indicating that the new device is ready to takeover as the new coordinator of the wireless network.